The present invention generally relates to methods and devices capable of monitoring environmental conditions, such as heat and/or humidity, including cumulative monitoring of heat and humidity. More particularly, this invention relates to a sensor in the form of a radio frequency identification (RFID) tag capable of measuring cumulative heat and humidity for continuous monitoring of storage and shipping conditions of items in various applications, including supply-chain management of perishable goods, pharmaceuticals, chemicals, and fresh agriculture products. The sensor RFID tag lends itself to automation and cost-effective supply chain management by using an RFID wireless link for transmission of cumulative sensor data to an RFID-reader (interrogator).
Environmental conditions, particularly accumulated exposure of an item to heat and humidity over time, have a conspicuous effect on the lifetime and operational capabilities of a wide variety of goods and products, notable examples of which include perishable consumer and healthcare goods such as food, medicine, vaccines, and blood bags, and military ordnance such as explosives, propellants, and solid rocket fuel. In both commercial and military applications, assuring functionality and/or the absence of deterioration, spoilage, etc., is extremely crucial, since otherwise lives could be at risk and substantial economic losses could incur. This sensitive need requires controlled shipping and storage environments in conjunction with assigning conservative expiration dates. However, the functionality and state of goods and products cannot be ensured without continuously monitoring environmental conditions, particularly heat and humidity, and the cumulative effects thereof.
Existing temperature and humidity sensors can be primarily categorized in two groups. A first of these is sensors based on change of color of a label in response to humidity and temperature. These sensor labels are relatively inexpensive and do not require a battery for power. However, significant shortcomings include being typically limited to indicating or recording only maximum (or minimum) temperature or humidity levels. Furthermore, while sensor labels provide an easily observable visual output, they lack an electronic interface and thus are difficult to deploy in automated supply chain management networks.
The second group of existing temperature and humidity sensors can be generally categorized as environmental parameter data logger modules that include individual humidity and temperature sensors, electronic chipsets for sensor interfacing and digitizing, a microcontroller, memory, a battery, and an external data communication link. Sensor modules of this type are generally capable of providing the necessary information to assess the functional and qualitative state of goods and products through continuously monitoring heat, humidity, and their cumulative effects. However, sensor modules are generally costly, have limited battery lifetime, are excessive in size for many applications, and require an additional (internal or external) software layer to provide a cumulative output. The high cost of these modules, particularly at an item-level, is a major barrier to their wide use in many applications.
In view of the above, it would be desirable if an environmental sensor system and method was available that overcame limitations and shortcomings of existing environmental sensor systems.